Manufacture of tufted carpets normally involves three basic operations: tufting a primary backing; washing, dyeing and drying the tufted backing; and then subjecting the same to a finishing operation.
Tufting usually is accomplished by inserting reciprocating needles threaded with yarn through the primary backing to form tufts or loops of yarn. Loopers or hooks, typically working in timed relationship with the needles, are located such that the loopers are positioned just above the needle eye when the needles are at an extreme point in their stroke through the backing fabric. When the needles reach that point, yarn is picked up from the needles by the loopers and held briefly. Loops or tufts of yarn result from the passage of the needles back through the primary backing. This process typically is repeated as the loops move away from the loopers due to advancement of the backing through the needling apparatus. If desired, the loops can be cut to form a cut pile, for example, by using a looper and knife combination in the tufting process. Alternatively, the loops can remain uncut.
In 1992, the total production of carpet in the United States was 1.3 billion square yards. Of that amount, 95% was made by tufting, with the remainder made by weaving. Major face yarn types currently used in the manufacture of tufted carpets are nylon yarns, normally composed of poly(epislon-caprolactam) or poly(hexamethylene adipamide), also known as nylon-6 and nylon 6,6, respectively; propylene polymer yarns, typically composed of propylene homopolymer; and polyester yarns, normally composed of polyethylene terephthalate. In 1993, according to Carpet & Rug Industry, October, 1993, page 6, the total United States carpet face yarn market was projected to be about 2.7 billion pounds. Nylon yarns accounted for about 68% of this market, polypropylene yarns for about 19%, and polyester yarns accounted for about 10%. Wool, cotton, acrylic, and other yarns accounted for about 3% of the total. Accordingly, it will be appreciated that the vast majority of carpets manufactured in the United States are tufted carpets, and that of all tufted carpets, the vast majority are manufactured with thermoplastic face yarns.
Primary backings for tufted carpets are typically woven fabrics made of synthetic yarns, although nonwoven fabrics can also be used. The most common synthetic material used in primary backings is polypropylene, although polyesters also find use in the industry. Again, it will be appreciated that the vast majority of backings for tufted carpets are manufactured from thermoplastics.
The carpet finishing operation typically involves application of a latex binder (typically a filled thermoset resin emulsion) and a secondary backing. According to “Carpet Laminating”, Journal of Coated Fabrics, Volume 19, July 1989, pp. 35-52, the material most typically used for carpet backcoating is styrene butadiene latex (SBR), usually a carboxylated SBR. The overwhelming majority of tufted carpet today is finished by laminating a secondary backing to the tufted primary with a latex.
More particularly, finishing is typically done in the following manner. The backside (i.e., the non-pile side) of a tufted primary backing is coated with a mixture containing a latex (100 parts), ground limestone or other inert particulate filler (300-500 parts), and processing aids such as surfactants, penetrants, defoamers, dispersants, chelating agents, stabilizers, and thickeners (1-3 parts). A woven polypropylene secondary backing is then attached to the backcoated tufted primary backing by passing the structure through a set of rolls, typically at the entrance to a large circulating air oven. The carpet is held taut on a tenter frame as it passes through the oven, setting the latex and driving off the water. The finished carpet then exits the oven, cools slightly by passing over a series of rolls, and is then inspected and taken up on a roll. While there are several variations on this basic process, such as the use of a “double-pan” to apply the latex binder mixture in two applications (the mixture in each application having a different viscosity), regardless of the method of application, the total latex binder weight is typically about 25-30 ounces per square yard. A typical line speed through the drying oven is 75 feet per minute.
Latex binders dominate the carpet industry because of their ability to provide good performance properties at low cost. Among the properties provided by the latex binders to the final carpet product are high tuft bind (anchoring of the yarn bundles), fuzz resistance (resistance of the fibers in the yarn bundles to being pulled out), and adhesion to the secondary backing (sometimes referred to as delamination or peel strength). These properties can be provided at a raw material cost for the latex binder mixture of roughly one cent per ounce per square yard, or about 25 cents per square yard for a typical carpet.